actually they are DIMMS. SIMMS are old technology. Also dont expect too much from celeron. It may get the job done for some tasks. Once you start using some vst's and plugings the performance will drop big time Believe me I work with PCs. An EMachine is a buget PC. Hey Im on a buget too. The Cheapest good PC right now would be a Dell.
Also before installing the ram tuch something metal to discharge any static. Although I've tried to distroy ram with static before I could not do it. I just wanted to see if it would fry.
Most PCs can take up to 2 gigs of ram even 4 gigs. You can buy it at Bestbuy, COMPUSA and most other places where PCs are sold. Beware of generic parts. I would recomend PNY Cheap, ULTRA a little more expensive, VIKING, yet more expensive. They have all worked good for me. If run into performance problems and want another computer I can recomend one for you.